1. Field of the Invention
The present invention is directed to a prosthetic attachment locking assembly which locks a residual limb stump to a prosthetic limb. More particularly, it relates to a prosthetic attachment lock incorporated into such an assembly.
2. Description of the Related Art
A prosthetic limb is conventionally secured to an amputee's residual limb stump by securing the prosthetic limb within a rigid socket part. This may commonly be done by shaping the socket such that it can form an air tight seal with the stump. In this case, a one way valve may be provided in the socket to permit air to be expelled from the socket as the stump is introduced, and the socket is held onto the stump by the resulting suction. While this is a comfortable form of suspension, an air leak due to stump shrinkage for example, can cause loss of suspension.
It is also known to secure the prosthetic limb to the stump by a lock pin. In this technique, the amputee first dons a sock-like sock liner formed of an elastomer with an optional fabric cover. The bottom end of the liner is formed of a rigid material such as urethane, and the lock pin extends from this rigid bottom. Such stump liners are well known, such as that manufactured and sold by The Ohio Willow Wood Company under the name Alpha Locking Liner. The pin is extended through the wall of the socket and a distal adapter mounted within or outside of the socket, and can be locked onto a prosthetic attachment lock mounted to the prosthetic limb to secure the prosthesis, optionally in conjunction with a suspension sleeve. Examples of a conventional locking assembly of this type are found in U.S. Pat. Nos. 5,507,837 and 5,888,234.
While conventional prosthetic attachment locking assemblies generally work well, they have a number of shortcomings. Amongst these is a tendency for the end of the lock pin to catch on a seam between the interior surface of the socket and the lip formed at the edge of the distal adapter when a distal adapter is fitted within the bottom of the socket. Another shortcoming is that the prosthetic attachment lock may also need to mate with the distal adapter through the intermediary of the bottom wall of the socket, which reduces the stability and structural rigidity of the joint. It is also necessary to use different distal adapters for test sockets which are made of a thermoplastic material, and definitive sockets which are made of a fiber reinforced laminate, and so it is necessary to use two kits for each prosthesis, which increases the final cost.
A further shortcoming of the conventional prosthetic attachment locks lies in the manner of releasing the lock pin from the locking device. Conventionally, the pin has a longitudinal series of rack-like serrations and extends through a pin bore of the lock body. The teeth of a pinion gear in the lock body extend into the pin bore to engage the teeth of the lock pin therein. The pinion gear is mounted for one way rotation to permit entry of the lock pin into the pin bore but lock the lock pin against removal. The lock pin can be released only by moving the pinion gear in a direction parallel to its rotational axis until it disengages from the lock pin, e.g., via a manual release button.
A problem with this conventional design is that the one way clutch incorporates the shaft onto which the pinion gear is mounted. Therefore, the force from the lock pin which has been tightened onto the gear is directly transferred to the gear shaft, which causes the shaft to bind and makes it difficult to manually push the manual release button sufficiently to release the lock pin.